: Can galvanized plumbers tape be used to secure brass shower valve against a 2X4? I know it can't be used for copper, but how about brass?

Technically, glavanized tape can be used against a brass pipe or fitting, for the fact is that brass nipples and fittings are allowed to be screwed into galvanized pipes and fittings. Just because that is allowed does not mean it's the best way to do things. In fact, such connections will corrode over long periods of time *tens of years). Brass is less electrolytically active than copper when connected to iron pipe, but it is still active. Note that there are many types of brass. Yellow brass has more zinc and less copper than red brass, and it is more prone to electrolytic "dezincification" than red brass.

Nonetheless, the fact that you've asked this question means that you realize there is a potential problem when dissimilar metals are mechanically connected to each other. So why would you do that and invite trouble when it would be very easy to avoid the problem altogether?